Turbomachines, in particular gas or steam turbines, have a rotor and blades which are coupled to the rotor and distributed around the circumference thereof. The blades must be designed to resist a plurality of stresses during operation of the turbine. Such stresses include, for example, centrifugal forces, erosion-corrosion, and vibrations.
The vibratory stresses to which the present invention relates may result from a combination of the medium passing through the turbine and the forces acting on the blades. In the long term, blade vibrations can cause a change in the microstructure of the blade material, which may eventually lead to a fatigue fracture. Therefore, it is necessary to damp the vibrations of the blades. In the prior art, a plurality of damping means for blade vibrations are known.
In German Patent Document DE 103 40 773, a damping means for a rotor blade of a turbine is disposed in a pocket of a rotor blade platform. The damping means has a triangle-like shape in a cross section normal to the axis and has rounded longitudinal edges. The longitudinal edges each have a symmetrically convex shape between the corners. During operation of the turbine, the damping means contacts an inner wall of the pocket and a friction surface of another rotor blade platform in order to damp movement of the rotor blade.
A disadvantage of the prior art damping means of symmetrically convex shape lies in the manner in which the region of frictional contact with a friction surface of the turbomachine is defined due to the symmetrically convex configuration of the longitudinal edge of the damping means. If the friction surface of the turbomachine has a particular shape, this may result in poor contact of the damping means with the friction surface of the turbomachine. For example, the friction surface of the turbomachine may be configured such that the damping means contacts the friction surface of the turbomachine only in a small region of frictional contact. As a result, the frictional heat produced during damping of the blade movement can only be dissipated through the small region of frictional contact, which may result in damage to or wear of the damping means and/or the corresponding friction part of the turbomachine.